IRAC Instrument Handbook - IRSA - California Institute of Technology

IRAC Instrument Handbook
band leaks are less than the astronomical background at all locations for sources of any temperature
detectable in the IRAC bands.
The spectral response curves presented below reflect our best knowledge of the telescope throughput and
detector quantum efficiency. The response curves use measurements of filter and beamsplitter
transmissions over the range of angles of incidence corresponding to distribution of incident angles across
the fields of view of the IRAC detectors (Quijada et al. 2004, Proc. SPIE, 5487, 244, [21]).
We provide three sets of curves for each IRAC channel: an average response curve for the entire array, an
average curve for the subarray field of view and a data cube of the response curves on a per pixel basis.
The average curves are useful for making color corrections to photometry of well-dithered (four or more)
observations. The response cubes can be used for more rigorous color corrections on per instance basis.
For most purposes, the average curves are sufficient. A more detailed discussion of the spectral response
curves is given by Hora et al. (2008, [14]). The derived IRAC spectral response curves are shown in
Figure 2.4. The IRAC web pages contain links to the tabulated spectral response curves.
Figure 2.4. Spectral res ponse curves for all four IRAC channels. The full array average curve is displayed in
bl ack. The subarray average curve is in green. The extrema of the full array per-pixel transmission curves
are also shown for reference.
Instrument Description 9 Description of Optics